It is sometimes desirable to simultaneously dispense two viscous paste or liquid materials which are reactant when in contact with one another. It is further desirable that such products be dispensed at a specific ratio for optimum performance. Pump type dispensers for two component products such as an epoxy and a hardener or a cosmetic and an activator are generally known. For example, U.S. Pat. No. 4,438,871 issued to Eckert on Mar. 27, 1984, discloses a push button style dispenser wherein two coaxial metering pistons are operated simultaneously and charges of product are simultaneously delivered from two individual pump chambers in quantities dependent upon the cross-section of the respective pistons. The intake of each of the individual pump chambers is ported into its own supply reservoir. Unfortunately, valve losses in smaller pumps tend to be greater than in larger pumps. It is therefore anticipated that the dispensed ratio of the two components in packages of this type will tend to vary. Consequently, one of the two product reservoirs is likely to be exhausted before the other.
One means to provide a specific product dispensing ratio and substantially simultaneous runout from a two component co-dispensing package is to displace the two components directly from their respective reservoirs with pistons which are caused to move simultaneously and equally. One such co-dispensing package for dispensing two materials in equal quantities is disclosed in U.S. Pat. No. 4,260,077 to Schroeder in April 1981. The dispenser of Schroeder consist of two joined parallel barrels and two joined plungers with attached pistons, one for each barrel. The distal ends of the plungers are joined to one another so that as the plunger assembly is advanced into the barrels, simultaneous and equal displacement of the pistons attached to the proximal ends of the plungers is assured. The result is substantially simultaneous dispensing of the two product components and also substantially simultaneous runout of the same. Unfortunately, co-dispensing packages of this sort are at least twice the length of the product chamber because of the need to externally join the plungers to one another. Further, since there is no mechanical advantage inherent in actuators of the type normally utilized on this type of dispenser, such dispensers are best suited to dispensing small quantities of product of relatively low viscosity with each stroke of the actuator.
U.S. Pat. No. 4,690,306 issued to Staheli on Sep. 1, 1987 discloses a dispensing device consisting of at least two chambers containing pasty substances, the pistons in the chambers being connected to one another by at least one blade oriented perpendicular to the product chambers and adapted for cutting through a dividing wall which separates the chambers from one another. One disclosed package embodiment employs a cartridge having two product components to be dispensed from coaxially arranged cylindrical chambers. The cylindrical chambers are partly closed at their forward end by a front wall. The central chamber is equipped with a circular piston and the outer chamber is equipped with an annular piston at their rearward ends. The pistons employed in the disclosed embodiment of Staheli are connected to one another by means of four radial blades having their sharp forward edges oriented perpendicular to the package's cylindrical axis and arrayed at angles of 90.degree. relative to each other. The blades allow the concentric pistons to advance in unison in their respective chambers by cutting through the internal wall between the outermost and central product chambers at the points where the blades contact the wall.
Because the blades of Staheli are arranged at right angles to the internal wall that is to be cut as the pistons advance, the blades must be sharp and comprised of a material which will cleanly cut the internal wall material without causing wrinkling or buckling of the internal wall.
Unfortunately, the foregoing functional compatibility requirement between the blades and the internal wall material of the package of Staheli is further complicated by the need for compatibility between the product components housed within the package and the wall material employed in the package structure, e.g., barrier properties, resistance to premature rupture, etc. All of the foregoing factors contribute toward increased cost and decreased reliability in the resulting package.